The conventional way to operate bicycles is to rotate the crank forward so that the wheels rotate forward. When the user stop to tread the pedals, the wheels still move forward by initial force and no work is output by the user. When the user rotates the crank backward, the wheels are not affected by the backward action because there is a ratchet mechanism in the hub.
The bicycle hub generally has a hub with bearings located therein, an axle extends through the hub and the bears. A socket unit is connected to the hub and a ratchet unit is connected to the socket unit. The socket unit is connected with a chain so that when the chain drives the socket unit, the ratchet unit is rotated which drives the hub to rotate in the same direction.
The ratchet units are cataloged by radial driving type and end driving type, wherein the radial driving type means that the first ratchet gear mounted to the socket unit and the second ratchet gear is located in the hub. The first and second ratchet gears are engaged with each other. The pawls rotate in the radial direction of the axle to contact the driving ratchet gear. The end driving type is also known as axial driving type, which means that the first ratchet gear is mounted to the end face of the socket unit and the second ratchet gear is located in the hub. The first and second ratchet gears are engaged with each other. The two ratchet gears are engaged in the axial direction of the axle.
Taiwan Patent Application No. 099104719 discloses an axle rotatably extends through a hub, a gear unit rotatably connected to the axle and located close to the hub. The gear unit has an inner end inserted into the hub, an outer end located in opposite to the inner end, and multiple grooves defined in the inner end and extending toward the outer end. The inner end has a bottom which define the grooves and multiple sidewalls extending radially from the bottom so as to be cooperated with the bottom to define the grooves. Multiple stepped portions extend from the sidewalls and located in the grooves. A clutch unit is located between the hub and the inner end of the gear unit. The clutch unit has a toothed ring located in the hub, multiple pawls pivotably connected to the grooves, and a resilient member located in the inner end and keeping the toothed ring and the pawls to move in one direction. The pawls respectively contact the stepped portions and are located by a gap from the sidewalls respectively.
Taiwan Utility Application No. 100219245 discloses a one-way ratchet unit which keeps the sprocket unit and the hub to rotate in one direction only. The ratchet unit comprises a first engaging portion connected to one end of the hub and having a first one-way ratchet gear which has multiple teeth each have a tip, a tool and two inclined guide sides. A second engaging portion is connected to an end of the sprocket unit and has multiple second one-way ratchet gear which has multiple teeth each have a tip, a tool and two inclined guide sides. The first and second one-way ratchet gears are engaged with each other in one directly. At least one resilient member is used to allow the first and second one-way ratchet gears to move over each other when the rotation direction is in opposite to the effective direction. At least one protrusion extends from the tip of the ratchet teeth of one of the first and second ratchet gears. The at least one protrusion extends along the inclined guide sides of the teeth. Those teeth without the at least one protrusion has a recess. At least one yield portion which is recessed in the root of the teeth of one of the first and second ratchet gears. When the first and second ratchet gears are engaged with each other, the recess is engaged with the at least one yield portion.
U.S. Pat. No. 6,123,179 discloses a bicycle freewheel hub and includes a hollow hub shell sleeved rotatably on a shaft, a cylindrical driving member sleeved rotatably on the shaft and disposed adjacent to the hub shell, and a clutch unit including first and second clutch members sleeved rotatably on the shaft. The first clutch member is coupled to the driving member. The second clutch member is coupled to the hub shell. Each of the clutch members has an annular end face which extends in a direction substantially perpendicular to the shaft. The annular end face of each of the clutch members has inclined teeth that are arranged annularly around the shaft and that project axially from the annular end face. The annular end face of the second clutch member confronts the annular end face of the first clutch member. The inclined teeth of the second clutch member engage the inclined teeth of the first clutch member when the driving member rotates in a first direction, and disengage therefrom when the driving member rotates in a second direction opposite to the first direction. A spring biases one of the first and second clutch members so as to keep interengagement of the first and second clutch members.
The first two Taiwan applications are radial driving type and the U.S. Pat. No. 6,123,179 is axial driving type. For the axial driving type hub, all of the ratchet teeth have to be engaged with each other to drive the hub so that the contact area of the ratchet teeth is larger than that of the radial driving type hub. Therefore, the axial driving type hub has better driving force. For the radial driving type hub, the distance of the driving position from the axle is longer than that of the axial driving type hub, so that the radial driving type hub saves effort.
For the radial driving type hub, there are three or four pawls are required on the socket unit and the pawls are pivotable radially to be engaged with the ratchet teeth on the hub. A resilient member is used to keep the pawls to be pivoted in one direction. However, the way that the pawl are pivoted to contact the individual ratchet tooth has slower linear movement than that of the axial driving type hub, so that the transmission of the driving force slightly delays. The four pawls provide limited contact area which provides less driving force and the tips of the pawls are easily worn out. When the tips of the pawls are damaged, the pawls may not able to contact the ratchet teeth to effectively drive the hub. If the four pawls have different levels of wearing, the stress will be concentrated at the tip of the pawl with less wearing, so that the driving force is not evenly spread on the four pawls. In other words, once one of the pawls is replaced, the rest of the three pawls have to be replaced. This means higher maintenance expense is required.
The present invention intends to provide a ratchet unit which is used for the radial driving type hub and provides larger driving force which is evenly spread to the ratchet teeth to increase the life of the ratchet unit.